Allele. A version, a sort, or a kind of a gene. For example, the gene for human earwax has two alleles, one for dry and one for wet.

Altruism. Behaving selflessly, at a cost to oneself but with a benefit to another.

Analogy. Similarity among organisms, which is the result of selection for their use in a similar function, not due to recent shared ancestry. It is the result of convergent evolution. For example, wings of butterflies, bats, and birds.

Ancient DNA (aDNA). Genetic material extracted from ancient remains that is almost always fragmented or damaged due to decomposition.

Anthropoid. Nickname for a member of the suborder anthropoidea, the so-called "higher primates," which includes monkeys, apes, and humans (but not tarsiers).

Anthropology. A broad, holistic, comparative science that is simply defined as the study of humans.

Arboreal. Tree-dwelling.

Archaeology. The study of people in the past and the cultural remains that they left behind.

Articulated. Connected. For example, when the bones of a skeleton are articulated, the thighbone articulates with the hipbone.

Atlatl. A spear thrower. The word was coined by the Aztecs but is used for all spear throwers no matter their origin, even those from archaeological sites that predate accounts of the Aztec weapons used against the Spanish.

Autosomes. All the nonsex chromosomes.

Bipedalism. Walking upright on the two hind legs. One who uses bipedalism for locomotion is said to have the trait of bipedality.

Blade. An Upper Paleolithic stone tool, which is at least twice as long as it is wide.

Bovid. A member of the family Bovidae, which is a diverse order of cloven-hoofed mammals including cows, antelope, buffalo, gazelles, sheep, and goats.

Brachiation. Locomotion by arm-swinging from tree branches. The Latin noun "brachium" means both arm and branch.

Canine-premolar (CP3) honing-complex. A system by which the upper canine is sharpened by the lower premolar when the teeth are in occlusion (i.e., the jaws are together). Carnivore. An animal that eats mostly meat.

Colobine. The leaf-eating subfamily of monkeys within the Old World monkeys or cercopithecoids.

Complex trait. One that is expressed by numerous genes.

Continuous trait. One that can exist over a range of variation, like height, for instance (for opposite see Discrete trait).

Core. A rock from which flakes are struck and used to make tools. Cranial capacity. The amount of space or volume in the skull that holds the brain and serves as a substitute for brain size when there is no brain present to measure its size directly. Cranial volume is often measured with grains of rice and is reported in cubic centimeters (cc).

Cranium (pl. Crania). The skull minus the mandible or jaw, which is often the state of fossil hominin specimens. When the cranium is missing the face and the base it is called a calotte or "skullcap." Cusp. In dental terms, cusps are peaks on premolars and molars. Dentition. Teeth.

Derived trait. One that is different from the ancestral or primitive form.

Discrete trait. One that can only exist in a finite number of states, for example, wet versus dry earwax (for opposite see Continuous trait).

DNA. Deoxyribonucleic acid. The molecule that makes up the genetic material in a cell's nucleus or mitochondria.

Drift. Also called "gene drift" or "genetic drift," it is a force of evolution where alleles are randomly spread throughout, or eliminated from a population in the absence of gene flow with other populations.

Ecology. The science or study of the relationships between organisms and their environments.

Endocast. Brains do not fossilize but the inside of a skull can fill with sediment. After many years, the resulting rock is a mold of the inside of the skull, resembling what the brain may have looked like during life. Scientists can also make endocasts by molding and casting the inside of skulls. Here endocast refers only to brains and skulls, but it is actually a more general term used for a variety of anatomical regions.

Evolution. Change in allele frequency through time.

Exaptation. A trait that natural selection favors for use in a different adaptation than that for which it was originally intended.

Fauna. Animals.

Fitness. Reproductive success.

Flora. Plants.

Foramen Magnum. Literally the "big hole" at the bottom of the skull for the exit of the spinal cord.

Founder effect. The result of a small subgroup of a population becoming isolated and starting a new population from a small gene pool. Frontal. Refers to either the skull bone at the forehead or to the right and left frontal lobes of the brain just underneath it.

Gene. Unit of DNA that codes for the development of a process or trait.

Gene flow. Mating between people of different populations, or the mixture of gene pools.

Gene pool. Breeding population.

Genome. The entire genetic sequence of an individual or species (based on a composite of individuals).

Genotype. The genetic makeup of an individual. It is unique to every person.

Genus (pl. Genera). Taxonomic grouping at one level above species that usually includes animals with a similar adaptive plateau.

Great ape. The hominoids excluding the lesser apes (gibbons and sia-mangs), which include orangutans, gorillas, chimpanzees, and bonobos. Some include humans under the umbrella term, some do not. Gregarious. Social or group-living (e.g., chimpanzees) as opposed to being solitary (e.g., orangutans).

Hand ax. The stone tool that typifies the Acheulean industry of the Pleistocene. It is teardrop shaped and is chipped away on both sides, also called a "biface."

Haplorhine. A member of the primate suborder Haplorhini ("dry noses") that includes tarsiers, New World monkeys, Old World monkeys, apes, and humans. The other suborder is Strepsirhini. Herbivore. A plant eater.

Heterozygote/Heterozygosity. When the two alleles at a genetic locus are different.

Hominid. "Hominin" is widely replacing this taxonomic term for humans and their unique fossil ancestors since the split from the chimpanzee lineage about 6 Mya.

Hominin. Any living human and all fossils on the unique lineage that led to humans after the split from the chimpanzee lineage about 6 Mya.

Hominoid. Apes and humans.

Homology. Similar in structure but not necessarily in function.

Homozygote/Homozygosity. When the two alleles at a genetic locus are the same.

Hypothesis. A prediction or a provisional explanation for a phenomenon that can be tested.

Isotope. A form of a chemical element in which the atoms have one or more extra neutrons.

Knuckle-walking. Mode of locomotion used by the African great apes and, to a degree, orangutans. Instead of putting the weight on the palm of the hand, like a crawling baby, knuckle-walkers put the weight on the middle phalanges of the hand. The same is not true for the foot, which hits the ground with the sole, however some apes do curl their toes under.

Kya. Thousands of years ago.

Last Common Ancestor (LCA). Also known as MRCA or the Most Recent Common Ancestor, the LCA is the shared ancestor between humans and chimpanzees before their evolutionary lineages split apart about 6 Mya.

Lesser ape. Gibbons and siamangs of Indonesia.

Life history. The developmental changes an organism experiences from conception to death.

Locomotion. The way an animal gets around and moves about.

Locus (pl. Loci). The location of a gene on a chromosome.

Long bones. The longest bones of the body, or the bones of the limbs, including the femur, tibia, fibula, humerus, radius, and ulna. Also, sometimes includes the metatarsals and metacarpals.

Macroevolution. Large-scale evolutionary changes, typified by speciation, above the population level. There is a false dichotomy between micro- and macroevolution since they are both located along the continuum of change that is driven by the same evolutionary forces.

Mandible. Lower jaw.

Maxilla. Upper jaw.

Meiosis. Division of gametes for reproduction.

Microevolution. Evolutionary change at the gene and trait level within a population. There is a false dichotomy between micro- and macroevolution since they are both located along the continuum of change that is driven by the same evolutionary forces.

Microwear. Tiny pits and scratches left on teeth by food. It can also refer to marks left on bones from teeth or stone tools, and also to marks left on stone tools from use.

Mitochondrial DNA (mtDNA). The DNA from the many mitochondria, or the "powerhouses," of the cell. It is the only DNA found outside of the nucleus.

Mitosis. Cell division everywhere in the body, except by the gametes, which divide by meiosis.

Molecular clock. A technique based on the clock-like rate of accumulation of mutations in DNA sequences, which is used to determine the time since two lineages diverged in evolution.

Monogamy. One male and one female form a pair-bond for reproducing and parenting.

Monogenic trait. One that is expressed by one gene (e.g., Mendelian inheritance).

Morphology. Technically, it is the study of the shape of something. It is also used as a synonym for shape and size. For example, tooth morphology of leaf-eating monkeys is much different than that of fruit-eating apes.

Mutation. A change in the genetic sequence in the daughter cell compared to the parent cell.

Mya. Millions of years ago.

Natural selection. A mechanism for evolution whereby favorable traits are spread to successive generations in a population by the survival and successful reproduction of individuals who have those favorable traits. Niche. An ecological strategy; a way of making a living. Offspring. The next generation of individuals produced by a male and a female.

Oldowan. The most primitive stone tool technology recognized by archaeologists, named for the site where thousands of early stone tools have been discovered: Olduvai Gorge, Tanzania.

Olduvai Gorge. A region in Tanzania with large-scale geologic outcrops containing fossil- and artifact-rich Pleistocene sediments. One of the "cradles of humankind."

Omnivore. An animal that eats a combination of plants, animals, and their products.

Ontogeny. Growth and development.

Opposable thumb. A thumb (digit 1) that is able to swing around, contact, and press firmly against, fingertip-to-fingertip with digits 2-5. Other primates, especially apes, can do this to a certain degree, but humans (partly because of joint mobility and partly because of finger lengths) have the most dexterous thumbs.

Paleoanthropology. The field of anthropology that studies human origins and evolution.

Platyrrhine. A member of the Platyrrhini ("flat, broad noses"), which are the New World monkeys.

Polygamy. A mating pattern by which an individual mates with more than one partner.

Polygenic trait. One that is expressed by multiple genes (see Complex trait).

Postcranium. The bones of the skeleton excluding the skull. In humans this is more like "beneath-cranium" but in most animals, the skeleton is located behind the skull, hence the use of "post."

Primitive trait. One that is shared because of shared ancestry. For example, five fingers and toes are primitive for mammals since humans, lemurs, raccoons, dogs, and cats, all have them even though these groups split deep in the mammal tree.

Prognathism. The state of having the face protrude out, away from the skull. "Gnath-" means jaw and the jaws make up much of the face. Dogs have extremely prognathic faces. Adult chimpanzees are much less prognathic, but are much more so than baby chimpanzees and humans.

Quadrupedalism. Locomotor category where the body weight is carried by all four limbs.

Reciprocity. "Tit for tat" behavior. Mutual exchange or cooperation. Robusticity/Robust. Strength, sturdiness, and thickness. Used here to describe the bones of the skeleton of certain species.

Sagittal crest. A raised bony ridge running along the uppermost cranium from the front to the back (i.e., in the sagittal plane) for the attachment of the chewing muscles.

Sexual dimorphism. Differences in physical characteristics in males and females. In the hominin fossil record, sexual dimorphism refers to body size, muscular attachment size, bone robusticity, and tooth size. But in modern animals this can refer to pigmentation differences, the presence of antlers, etc.

Sexual selection. Another means, besides natural selection for evolution to occur, by which individuals choose mating partners according to such things as fitness indicators.

Somatic cells. Cells that make up the body including those specific to skin, muscle, blood, and bone.

Speciation. Allopatric (speciation by way of physical, spatial separation of groups, preventing them from mating with one another).

Stature. The height of a person.

Strepsirhine. Amember of the primate suborder Strepsirhini ("wetnoses"), which includes lemurs and lorises. The other suborder is Haplorhini.

Taphonomy. All of the decompositional and other processes a bone or fossil undergoes between the time of death of the organism and the time until it is recovered.

Taxon (pl. Taxa). A group of organisms that share certain attributes at any taxonomic level (like kingdom, phylum, order, family, genus, and species).

Taxonomy. The classification of living things into natural orders according to their relatedness and similarities. The science of classification. Terrestrial. Ground-dwelling or adapted for moving about on the ground. Tetrapoda. Class of animals within the vertebrates that includes four-legged walkers (e.g., crocodiles, monkeys, lizards, horses) and those with four-legged walkers in their ancestry (e.g., birds, humans, snakes, whales).

Thorax. The torso or trunk of the body.

Trophic pyramid. Also known as the "food chain." It is the ecological ordering of a community of animals in the never-ending food energy cycle where higher members eat lower members and they, in turn, are preyed upon by even higher members. It takes the form of a pyramid because there are less and less animals per group as one moves up. The top of the pyramid holds the carnivores and they are the least populous in any given community. Vertebrates. Animals of the subphylum Vertebrata that are characterized by having a backbone and include fishes, amphibians, reptiles, birds, and mammals.